1. Field of the Invention
The present invention generally relates to a pump for feeding a liquid and, more particularly, to a pump having a gas removal function for removing gaseous contaminants contained in the liquid to thereby feed the liquid containing little gaseous contaminants.
2. Description of the Prior Art
In various fields of industry, a requirement exists to remove gaseous contaminants contained in a liquid which are fed by a pump. One example can be found in a chemical industry where raw materials, intermediate products or final products in the form of liquid are fed by the pump to be processed and/or stored. These liquid materials and products often contain gaseous contaminants which cause problems during feeding, processing and at the final products and should therefore be removed. Also, various lubricating oils tend to contain gaseous contaminants during use, examples thereof including oils for use in engine, gear, automatic transmission, torque converter, power steering, hydraulic actuator, turbine, compressor, quenching, rolling, metal working and traction device. Such gaseous contaminants adversely affect the lubrication and hydraulic properties and are desired to be removed.
There has been a known technique which utilizes a buoyancy of gases for removing the contaminants from the liquid. Another approach has resulted in a use of centrifugal force generated by a vortex flow of the liquid as disclosed in, for example, Japanese Patent Publications Nos. 44-23803 and 61-36444 and Japanese Patent Laid-Open No. 1-104315. Due to a difference in density, the gas-rich liquid having a smaller specific gravity gathers in an area around a center of the vortex flow and the liquid containing little gaseous contaminants is separated to gather in a peripheral area.
However, all of the known gas removal devices are provided separately from a pump for feeding the liquid, and nothing has hitherto been proposed toward an integration of the pump and gas removal device. To install the pump and gas removal device in different portions of feed pipes of a chemical plant or lubricating system necessarily involves not only an increased work but also an increased space for the assembly and is therefore undesirable. This is particularly important when only a limited space is available for installation, such as in an automobile engine and an automatic transmission where miniaturization is one of the essential requirements in a design.